|  | 4.5 | Layer 3 Design
| 4.5.3 | Explain how a router provides structure to a network
Routers provide scalability because they can serve as firewalls for broadcasts. In addition, because Layer 3 addresses typically have structure, routers can provide greater scalability by dividing networks and subnets, therefore, adding structure to Layer 3 addresses. The ways in which greater scalability in networks can occur are shown in the table. When the networks are divided into subnets, the final step is to develop and document the IP addressing scheme to be used in the network. Routing technology filters data-link broadcasts and multicasts. By adding router ports with additional subnet or network addresses, you can segment the internetwork as required. Network protocol addressing and routing provide built-in scaling. When deciding whether to use routers or switches, remember to ask, "What problem am I trying to solve?" If your problem is protocol related rather than contention oriented, then routers are appropriate. Routers solve problems with excessive broadcasts, protocols that do not scale well, security issues, and network-layer addressing. Routers, however, are more expensive and harder to configure than switches.